In recent years, magnetic disc devices or the like have tended toward higher densities, and accompanying this, a magnetic head based on a high magnetic resistance effect (hereinafter referred to as a "MR head") has been used in many cases. To accommodate such magnetic disc devices, the magnetic recording medium must also exhibit excellent magnetic properties such as low noise.
This is because the MR head has high read sensitivity and low head noise as compared with conventional magnetoelectric induction type heads. For improving the properties of the magnetic disc device and the like, such as S/N ratio and recording density, the magnetic recording medium must also have excellent magnetic properties such as low noise properties.
The magnetic recording medium commonly used at present comprises a substrate comprising an Al alloy having formed thereon an NiP plating film, a non-magnetic undercoat film comprising Cr or the like formed on the substrate, a magnetic film comprising a material containing Co as a main component formed on the undercoat film, and a protective film and a lubricant film formed thereon.
This kind of magnetic recording medium is disclosed in JP-B-5-24564 (the term "JP-B" as used herein means an "examined Japanese patent publication"). The magnetic recording medium disclosed in this patent publication exhibits improved squareness by providing a non-magnetic undercoat film comprising Cr and having a thickness of from 50 to 200 .ANG..
Furthermore, JP-A-1-232522 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes a magnetic recording medium including a non-magnetic undercoat film comprising an alloy obtained by adding one or more metals selected from Cu, Nb, Ti, V, Zr, Mo, Zn, W and Ta to Cr and having a thickness of from 500 to 3,000 .ANG., to thereby improve magnetic properties, particularly coercivity.
However, in the magnetic recording medium disclosed in JP-B-5-24564, the thickness of the non-magnetic undercoat film comprising Cr is small and accordingly, the crystals growing in this undercoat film are not sufficiently oriented toward the (200) direction. As a result, orientation of the crystals within the magnetic film, which epitaxially grow on the undercoat film, is disordered and the magnetic recording medium thus obtained disadvantageously fails to provide satisfactory magnetic properties such as coercivity.
In the magnetic recording medium disclosed in JP-A-1-232522, the thickness of the non-magnetic undercoat film comprising a Cr alloy is large and at the time of forming the film, bulking of crystals comprising a Cr alloy takes place within the film. In turn, magnetic grains within the magnetic film formed on the non-magnetic undercoat film are bulked due to epitaxial growth on the non-magnetic undercoat film comprising the bulked Cr alloy crystals. As a result, the magnetic recording medium thus obtained disadvantageously has deteriorated magnetic properties such as deteriorated noise properties.
The present invention has been achieved in view of the above problems of the prior art.